So if I go from 650 to $1000/mo on a mortgage, I'm down to about $500 before allowances/$250 with it (even if you said that another $150 of that is going to principal, that doesn't exactly solve my problem of having too much cash still locked away in the house). 

Using the 50% principal half goes to expenses and half for profit and mortgage expense.

In other words, if I took proceeds from both sales (400k on principal residence, and 250k from investment property), and purchase a new home (for myself) for 650k, will I be expected to pay capital gains on the value increase from my investment property (bought for 150k, now valued at 250k)?

Please be sure to select a Solo 401k plan provider which allows you to take a loan and will prepare the required 401k loan documents.The repayment terms are equal monthly/quarterly payments (as you prefer) of principal and interest (e.g. prime + 1%) spread over a 5 year term (or longer if you will use the loan to purchase your primary residence). 

My cash flow math isGross rents - 30% (vac, maint, and capex) - PITI (principal, interest, taxes, and ins) = true long term cash flow.I recognize that this math does not work in many areas of the country.

Just enter the principal amount and the rate and it will give it to you. 

Do you want to plunk down down payments in return for monthly cash flow, tax benefits, and principal pay down?

If I have $15,000 into the property monthly payments estimate to about $308/month (Principal, Interest, Prop.

My understanding if you owned the home and sold, even if it was given to you, you aren't eligible.https://www.fin.gov.on.ca/en/bulletins/ltt/1_2008.htmlRequirements to qualify for the refundTo qualify for a refund: The purchaser must be at least 18 years old.The purchaser must occupy the home as their principal residence within nine months of the date of transfer.The purchaser cannot have ever owned an eligible home, or an interest in an eligible home, anywhere in the world, at any time.If the purchaser entered into an agreement of purchase and sale before December 14, 2007, the home must be a newly constructed home and the purchaser must be eligible for the Tarion New Home Warranty.If the purchaser has a spouse, the spouse cannot have owned an eligible home, or had any ownership interest in an eligible home, anywhere in the world, while he or she was the purchaser's spouse.

Both have inherent risks, levels of influence available to an investor, and the possibility of principal lost.The level of “control” you feel you may have over real estate does not negate the fact that there things you cannot control.